The vagus nerve slow heart rate in part by activating a cardiac potassium (K+) channel, I/KACH- Activated muscarinic receptors release the G protein Gbetagamma dimer which dramatically increases channel activity by up to 1,000-fold. We showed that I/KACH was composed of two distinct inwardly rectifying K+ channel subunits, KIRK1 (Kir3.1) and GIRK4 (KIR 3.4). In this proposal we outline the experiments that over the next five years will reveal the assembly expression, and stabilization of the cardiac I/KACh channel. First, we will use a combination of electrophysiology, biochemistry, and molecular biology to study how the GIRK1/GIRK4 subunits assembly and determine proteins associating with the final complex. In particular we are interested in how a particular receptor maintains its specificity of activation of the channel. Second, evidence indicates that key lipids are important to the regulation and stability of the final channel complex once it has reached the plasma membrane. We will refine our understanding of the role of Gbetagamma and phosphatidylinositols in the regulation of the functional GIRK1/GIRK4 complex. Finally, we will characterize the promoters of GIRK channel subunits in preparation for defining transcriptional control of their expression. One major question is why IKACh is preferentially expressed in pacing tissues and atria, but not ventricle. If we can understand the details of expression, assembly, and regulation of this channel, it may someday be possible to selectively express and activate it in order to terminate firing of excitable cells in arrhythmias.